The present invention relates to a process for the preparation of formate salt from biomass and to the product obtained thereof.
Biomass such as pulp, waste paper, paper mill sludge, urban waste paper, agricultural residues, rice straw, woody plant, cotton materials and cellulose fines from papermaking etc. may be reconverted into useful platform chemicals. This requires sufficient economics and reasonable process feasibility for the processes to be used for the recovery of industrially interesting chemicals.
A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of biomass such as cellulose which is a natural polymer consisting of glucose units and abundantly available on earth. One attractive option is the conversion of glucose to levulinic acid (IUPAC systematic name: 2-hydroxypropanoic acid i.e. 4-oxopentanoic acid i.e. acetyl propanoic acid) by acid treatment. In the following text, the trivial name levulinic acid is used as the name of this compound. Levulinic acid is a versatile building block for fuel additives, polymers, and resin precursors.
Two different approaches are commonly applied for the acid-catalyzed hydrolysis of cellulose. The first one uses high concentrations of mineral acids (e.g., 15-16 N HCl or 31-70% by weight H2SO4) as catalysts at low operating temperatures (20-50° C.). The major drawbacks are the high operating cost of acid recovery and the use of expensive construction material for both the hydrolyser and the acid recovery system. The second approach uses highly diluted acids at high operating temperatures (170-240° C.). This method is favoured and research studies applying this approach are abundant.
There are several publications on conversion of biomass to carboxylic acids but none of them simultaneously recover both levulinic acid and formic acid economically and selectively with sufficient purity. Most of the publications disclose methods for converting carbohydrate material to organic acids such as levulinic acid and formic acid, and furfural. A purification process especially to formic acid is not described in the procedures of converting biomass in the literature.
Several publications disclose the separation and recycling of formic acid or more typically carboxylic acids in general, and levulinic acid or furfural from the mixtures thereof. The actual recovery of formic acid as concentrated formic acid or as formate ester or salt as such originating from biomass with suitable purity for further applications could not be found.
In the article of Hayes et al. in Kamm, Gruber, Kamm: Biorefineries—Industrial Processes and Products, Vol. 1, p. 139-164, it is mentioned that the processing of cellulose yields approximately 50% of levulinic acid, 20% of formic acid, and 30% of tars calculated from the mass of 6-carbon sugars. The mass yield of furfural from 5-carbon sugars is approximately 50%. Thus, each ton of levulinic acid produced produces 400 kg of formic acid. There is clearly a need to recover efficiently and simultaneously formic acid parallel to the other platform chemicals.
Formic acid may be recovered in acid form or as a formic acid derivative such as formate ester or salt.
WO2005070867 discloses a reactive extraction method for the recovery of levulinic acid from an aqueous mixture containing e.g. levulinic acid, formic acid and furfural wherein the mixture is first contacted with a liquid esterifying water-immiscible alcohol in the presence of a catalyst at 50 to 250° C. to form esters of levulinic acid and formic acid. These esters remain in organic phase together with the alcohol and furfural. According to the invention, the desired levulinate and all the other compounds can be separated by applying different sequential separation methods, distillations such as e.g., reactive distillation from the organic phase. Formic acid ester is converted to formic acid by acid hydrolysis and separated simultaneously by distillation from the alcohol. This separation process has not been experimentally verified and is known to be very complex. Formic acid is equally obtainable as an ester from the organic phase requiring further processing for the recovery of the pure acid.
In many cases, the carboxylic acids generated as the result of biomass degradation are obtained as dilute aqueous solutions. Distillation is an obvious method to purify isolated substances from aqueous solutions, but distillation as such is not the best option as far as energy-efficiency is considered. Besides, some of the components such as formic acid may form azeotropes with water making the separation into pure components difficult. The separation can be accomplished by arranging several distillation processes and equipment parallel or in series but then the energy cost of separation and equipment will become high. Furthermore, separation into single components is not feasible without using large distillation columns with a high number of separation stages or trays.
Separation of various chemicals may be based on liquid-liquid extraction processes. Even carboxylic acids have been separated from dilute aqueous solutions with extraction solvents insoluble or slightly soluble in water, or with solvent mixtures. However, the efficiency of extraction agents is typically not satisfactory enough to yield pure components.
The solution obtained from biomass degradation, e.g., hydrolysis at elevated temperature and pressure, can contain furfural if the raw material includes pentoses. Furfural in these cases can be converted to its derivatives, such as furfuryl alcohol, methyl furfuryl alcohol, methylfuran, furoic acid, furfurylamine, furan, and their further derivatives. Catalytic hydrogenation of furfural to methyl furan and further into methyltetrahydrofuran or to furfuryl alcohol and further into levulinic acid is mentioned in the literature.
Prior art discloses several ways of recovering industrially valuable components from biomass degradation including furfural or levulinic acid. Aqueous carboxylic acids or mixtures thereof may be separated and/or circulated back to earlier processes stages. Reference is made to patent publications such as WO02053521, WO0146520, EP0038317, and the like.
Neutralization reactions with appropriate alkaline materials are usually applied in order to prepare salt materials from acids. For example, hydrochloric acid and sulphuric acid react with metal oxides, metal hydroxides and metal carbonates to make salts. If the solutions contain several acid components as constituents, the neutralization brings about a mixture of several salts some of which may even precipitate depending on the solubility. The purification or recovery of some specific salt compounds from this kind of multisalt mixtures is very difficult. If multicomponent acid mixtures originating from biomass disintegration processes would be subjected directly to neutralization treatment, multiple salts would be obtained and the recovery of any of the individual acids as pure salt material would be severely complicated and thus uneconomical.
The objective of the present invention is to provide a method for economically and efficiently recovering formic acid in formate salt form from a biomass degradation mixture.
A further objective of the present invention is to provide a method for economically and efficiently recover formic acid in formate salt form together with levulinic acid and optionally furfural from an aqueous mixture of formic acid, levulinic acid and optionally furfural.
Yet, a further object of the present invention is to provide good quality ammonium formate suitable for industrial use.